Cleaning robots are apparatuses that suction dust accumulated on a surface while hovering over a space to be cleaned, thereby automatically cleaning the space without an operation by a user. That is, cleaning robots clean space to be cleaned while hovering over the space.
Generally, to sense surrounding obstacles and measure distances from obstacles, robot cleaners emit ultrasonic waves or infrared rays, sense the ultrasonic waves or infrared rays reflected by obstacles, determine the presence of obstacles or distances thereto based on time differences, phase differences, or level differences of the sensed signals or also determine the distances using reflection angles. Recently, a light emitting portion emitting ultrasonic waves or infrared rays and a light receiving portion sensing ultrasonic waves or infrared rays reflected by obstacles and returning are installed as unit modules. Here, space in which modules are located is necessary and each of the light emitting portion and the light receiving portion is necessary, thereby increasing manufacturing cost. Also, since a module capable of emitting signals only forward and sideward is installed, it is impossible to sense obstacles in a blind spot beyond a range of signal, that is, an obstacle located above.